1. Field of the Invention
This invention generally relates to a composite cooking system and, more particularly, to a composite cooking apparatus capable of performing microwave heating as an electronic range apparatus, electromagnetic induction heating as an electromagnetic cooking apparatus, and a method of controlling the same.
2. Description of the Related Art
A composite cooking system with an inverter circuit has been developed which is capable of performing microwave heating in an electronic range and electromagnetic induction heating in an electromagnetic cooking system.
In addition to the advantages of two heating functions, the composite cooking system can use a lightweight, compact high-voltage transformer as compared with that in the electronic range.
In such a composite cooking system, however, many problems are left unsolved.
In a composite cooking system, when output level control during microwave heating is not sufficient, output (power consumption) is decreased due to a change in temperature of a magnetron or the like, and optimal heating is often difficult.
A so-called standard cooking utensil such as a pot or a pan is used to control the output (power consumption) of electromagnetic induction heating during manufacturing. However, various types of cooking utensil are commercially available, and a higher output (power consumption) than that preset with the standard pan may be generated in practice. In this case, elements of an inverter circuit are overloaded to adversely affect the service life and cause operation failure.
In the above composite cooking system, a pan as a load must be discriminated to be an optimal load during induction heating. If the load as the pan is not appropriate, the operation of the inverter circuit must be immediately interrupted to assure safe operation.
A load detector may be arranged as in the conventional electromagnetic cooking system. However, a large number of components are required, resulting in a high cost. In addition, control of the load detector is difficult.
The conventional composite cooking system has a further problem. At the start of heating, output from the inverter circuit is increased to a preset level However, at the start of microwave heating, a heater of the magnetron is not sufficiently heated. Therefore, the anode voltage of the magnetron is increased, and stress (overvoltage) acts on the associated high-voltage diode and capacitor.
More specifically, at the start of microwave heating, the level of the output setting signal is increased to increase the output from the inverter circuit to the preset output. At this time, the anode voltage of the magnetron is greatly increased. It should be noted that an input current is a current input to the inverter circuit.
For the above reason, expensive components which can widthstand an overvoltage must be used as the high-voltage diode and capacitor, resulting in a high cost.
In such a composite cooking system, a common timer is generally used for controlling the cooking time, and a common operation knob for setting the cooking time is generally used.
The cooking time for microwave heating is relatively short, while that for induction heating is relatively long. Therefore, an operation for setting the cooking time for induction heating is cumbersome.